Andrographolide induces protective autophagy and targeting DJ-1 triggers reactive oxygen species-induced cell death in pancreatic cancer.

Background: Andrographolide (Andro), an extract of Andrographis paniculate (Burm.f.) Wall. ex Nees (Acanthaceae), possesses diverse biologically active properties. However, the precise mechanisms and effects of Andro on pancreatic cancer (PC) remain unclear. Methods: The cytotoxic potential of Andro and underlying mechanism towards PC cells was investigated through in vitro experiments and a xenograft mouse model. PC cells were first subjected to varying concentrations of Andro. The reactive oxygen species (ROS) was assessed using flow cytometry and DCFH-DA staining. The apoptosis rate was detected by flow cytometry. Additionally, western blot was applied to evaluate the expression levels of cleaved-caspase-3, DJ-1, LC3-I, LC3-II, and p62. To further elucidate the involvement of ROS accumulation and autophagy, we employed N-acetylcysteine as a scavenger of ROS and 3-Methyladenine as an inhibitor of autophagy. Results: Andro demonstrated potent anti-proliferative effects on PC cells and induced apoptosis, both in vitro and in vivo. The cytotoxicity of Andro on PC cells was counteracted by DJ-1 overexpression. The reduction in DJ-1 expression caused by Andro led to ROS accumulation, subsequently inhibiting the growth of PC cells. Furthermore, Andro stimulated cytoprotective autophagy, thus weakening the antitumor effect. Pharmacological blockade of autophagy further enhanced the antitumor efficacy of Andro. Conclusion: Our study indicated that ROS accumulation induced by the DJ-1 reduction played a key role in Andro-mediated PC cell inhibition. Furthermore, the protective autophagy induced by the Andro in PC cells is a mechanism that needs to be addressed in future studies.

Jolkinolide B attenuates allergic airway inflammation and airway remodeling in asthmatic mice.

Asthma is a widely prevalent chronic disease that brings great suffering to patients and may result in death if it turns severe. Jolkinolide B (JB) is one diterpenoid component separated from the dried roots of Euphorbia fischeriana Steud (Euphorbiaceae), and has anti--inflammatory, antioxidative, and antitumor properties. However, the detailed regulatory role and associated regulatory mechanism in the progression of asthma remain elusive. In this work, it was demonstrated that the extensive infiltration of bronchial inflammatory cells and the thickening of airway wall were observed in ovalbumin (OVA)-induced mice, but these impacts were reversed by JB (10 mg/kg) treatment, indicating that JB relieved the provocative symptoms in OVA-induced asthma mice. In addition, JB can control OVA-triggered lung function and pulmonary resistance. Moreover, JB attenuated OVA-evoked inflammation by lowering the levels of interleukin (IL)-4, IL-5, and IL-13. Besides, the activated nuclear factor kappa B (NF-κB) and transforming growth factor-beta-mothers against decapentaplegic homolog 3 (TGFß/smad3) pathways in OVA-induced mice are rescued by JB treatment. In conclusion, it was disclosed that JB reduced allergic airway inflammation and airway remodeling in asthmatic mice by modulating the NF-κB and TGFß/smad3 pathways. This work could offer new opinions on JB for lessening progression of asthma.

[Effect of triptolide on reproductive toxicity in female rats with â ¡ type collagen induced arthritis].

In order to study the toxic effect and mechanism of triptolide(TP) on the reproductive system of female rats with Ⅱ type collagen induced arthritis(CIA), 50 SD rats were randomly divided into normal control group, CIA model group, and three groups receiving TP tablets at clinically equivalent doses of 0. 5, 1, and 2 times, respectively(with TP dosages of 3. 75, 7. 5, and 15 µg·kg~(-1)·d~(-1)), each comprising 10 rats. Intragastric administration was started on the day after the first immunization, once a day, for 42 days.The results were taken on the 21st and 42nd days to calculate the uterine and ovarian organ indexes; pathological and morphological changes in uterus and ovaries were observed under a light microscope; and the levels of estradiol(E_2) and cytochrome P450A1(aromatase,CYP19A1) in ovarian homogenate were detected by ELISA. Furthermore, immunohistochemistry was employed to detect the expression levels of transforming growth factor ß3( TGFß3) pathway-related proteins, mothers against decapentaplegic homolog 3(Smad3) and steroidogenic factor-1(SF-1) in ovarian tissues. In vitro, the mouse Chinese hamster ovary(CHO) cell line was established, and after 24 hours of TP administration(30, 60, 120 nmol·L~(-1)), cell proliferation was detected by the thiazolyl blue tetrazolium bromide(MTT) method, apoptosis by the flow cytometry, and TGFß3, Smad3 and SF-1 protein expression in cells by the Western blot method, and the nuclear entry of SF-1 was detected by immunofluorescence. The results showed that compared with the CIA model group, all TP administration groups showed decreased number of uterine glands, total follicles, mature follicles, and corpus luteum on days 21 and 42 of administration, but there was no statistical difference, and only the administration of 2 times the clinically equivalent dose of TP could significantly increase the number of atretic follicles at 42 days of administration. TP at 3. 75 µg·kg-1·d-1significantly reduced the level of E_2 at 21 days of administration and the expression of TGFß3 and Smad3 factors in ovarian tissues,but had no significant effect on the rate-limiting enzyme in estrogen synthesis CYP19A1. TP at 7. 5 and 15 µg·kg~(-1)·d~(-1) significantly reduced the expression of SF-1 regardless of administration for 21 days or 42 days. TP can significantly promote ovarian cell apoptosis in vitro, with apoptosis mainly concentrated in the late stage of apoptosis after 24 hours of administration. In addition, 60 nmol·L~(-1) TP significantly reduced the protein expression of TGFß3, Smad3 and SF-1 in a dose-dependent manner. In summary, intragastric administration of TP at less than 2 times the clinically equivalent dose for 21 days and 42 days did not cause obvious reproductive damage to the uterus and ovarian tissues of CIA rats, and the number of atretic follicles changed significantly only when the 2 times the clinically equivalent dose was administered for 42 days. TP exerted reproductive toxicity in vivo on reproductive target organs and in vitro on ovarian cells by inhibiting the expression of TGFß3/Smad3/SF-1 pathway.

Combination of Pirfenidone and Andrographolide Ameliorates Hepatic Stellate Cell Activation and Liver Fibrosis by Mediating TGF-ß/Smad Signaling Pathway.

Background: Biliary atresia (BA) is a devastating congenital disease characterized by inflammation and progressive liver fibrosis. Activation of hepatic stellate cells (HSCs) plays a central role in the pathogenesis of hepatic fibrosis. Our study aimed to investigate the pharmacological effect and potential mechanism of pirfenidone (PFD) and andrographolide (AGP) separately and together on liver fibrosis of BA. Materials and Methods: The bile ducts of male C57BL/6J mice were ligated or had the sham operation. The in vivo effects of PFD and/or AGP on liver fibrosis of BA were evaluated. Human hepatic stellate cells (LX-2) were also treated with PFD and/or AGP in vitro. Results: PFD and/or AGP ameliorates liver fibrosis and inflammation in the mice model of BA, as evidenced by significant downregulated in the accumulation of collagen fibers, hepatic fibrosis markers (α-SMA, collagen I, and collagen IV), and inflammatory markers (IL-1ß, IL-6, and TNF-α). Moreover, compared with monotherapy, these changes are more obvious in the combined treatment of PFD and AGP. Consistent with animal experiments, hepatic fibrosis markers (α-SMA, collagen I, and CTGF) and inflammatory markers (IL-1ß, IL-6, and TNF-α) were significantly decreased in activated LX-2 cells after PFD and/or AGP treatment. In addition, PFD and/or AGP inhibited the activation of HSCs by blocking the TGF-ß/Smad signaling pathway, and the combined treatment of PFD and AGP synergistically inhibited the phosphorylation of Smad2 and Smad3. Conclusion: The combined application of PFD and AGP exerted superior inhibitive effects on HSC activation and liver fibrosis by mediating the TGF-ß/Smad signaling pathway as compared to monotherapy. Therefore, the combination of PFD and AGP may be a promising treatment strategy for liver fibrosis in BA.

Discovery of a terpene synthase synthesizing a nearly non-flexible eunicellane reveals the basis of flexibility.

Eunicellane diterpenoids, containing a typical 6,10-bicycle, are bioactive compounds widely present in marine corals, but rarely found in bacteria and plants. The intrinsic macrocycle exhibits innate structural flexibility resulting in dynamic conformational changes. However, the mechanisms controlling flexibility remain unknown. The discovery of a terpene synthase, MicA, that is responsible for the biosynthesis of a nearly non-flexible eunicellane skeleton, enable us to propose a feasible theory about the flexibility in eunicellane structures. Parallel studies of all eunicellane synthases in nature discovered to date, including 2Z-geranylgeranyl diphosphate incubations and density functional theory-based Boltzmann population computations, reveale that a trans-fused bicycle with a 2Z-configuration alkene restricts conformational flexibility resulting in a nearly non-flexible eunicellane skeleton. The catalytic route and the enzymatic mechanism of MicA are also elucidated by labeling experiments, density functional theory calculations, structural analysis of the artificial intelligence-based MicA model, and mutational studies.

Telescoping a Prenyltransferase and a Diterpene Synthase to Transform Unnatural FPP Derivatives to Diterpenoids.

New diterpenoids are accessible from non-natural FPP derivatives as substrates for an enzymatic elongation cyclization cascade using the geranylgeranyl pyrophosphate synthase (GGPPS) from Streptomyces cyaneofuscatus and the spata-13,17-diene synthase (SpS) from Streptomyces xinghaiensis. This approach led to four new biotransformation products including three new cyclododecane cores and a macrocyclic ether. For the first time, a 1,12-terpene cyclization was observed when shifting the central olefinic double bond toward the geminial methyl groups creating a nonconjugated 1,4-diene.

The wide spectrum anti-inflammatory activity of andrographolide in comparison to NSAIDs: A promising therapeutic compound against the cytokine storm.

The challenges of the COVID-19 pandemic have highlighted an increasing clinical demand for safe and effective treatment options against an overzealous immune defence response, also known as the "cytokine storm". Andrographolide is a naturally derived bioactive compound with promising anti-inflammatory activity in many clinical studies. However, its cytokine-inhibiting activity, in direct comparison to commonly used nonsteroidal anti-inflammatory drugs (NSAIDs), has not been extensively investigated in existing literature. The anti-inflammatory activities of andrographolide and common NSAIDs, such as diclofenac, aspirin, paracetamol and ibuprofen were measured on lipopolysaccharide (LPS) and interferon-γ induced RAW264.7 cells. The levels of PGE2, nitric oxide (NO), TNF-α & LPS-induced release of pro-inflammatory cytokines on differentiated human macrophage THP-1 cells were measured against increasing concentrations of andrographolide and aforementioned NSAIDs. The associated mechanistic pathway was examined on NFκB using flow cytometry on the human endothelial-leukocyte adhesion molecule (ELAM9) (E-selectin) transfected RAW264.7 cells with green fluorescent protein (GFP). Andrographolide exhibited broad and potent anti-inflammatory and cytokine-inhibiting activity in both cell lines by inhibiting the release of IL-6, TNF-α and IFN-γ, which are known to play a key role in the etiology of cytokine storm and the pathogenesis of inflammation. In comparison, the tested NSAIDs demonstrated weak or no activity against proinflammatory mediators except for PGE2, where the activity of andrographolide (IC50 = 8.8 µM, 95% CI = 7.4 to 10.4 µM) was comparable to that of paracetamol (IC50 = 7.73 µM, 95% CI = 6.14 to 9.73 µM). The anti-inflammatory action of andrographolide was associated with its potent downregulation of NFκB. The wide-spectrum anti-inflammatory activity of andrographolide demonstrates its therapeutic potential against cytokine storms as an alternative to NSAIDs.

Blocking smoothened cholesterylation: A strategy for overcoming drug resistance in cancer.

In this issue of Cell Chemical Biology, Liu et al.1 report the identification of Q29, a synthetic diterpenoid that blocks covalent cholesterol modification of smoothened (SMO) and inhibits hedgehog signaling. Q29 is capable of suppressing tumor cell growth, both in vitro and in vivo, and overcoming resistance to SMO inhibitors.

Extraction optimization and reactivity of 7α-acetoxy-6ß-hydroxyroyleanone and ability of its derivatives to modulate PKC isoforms.

Protein kinase C is a family of kinases that play important roles in carcinogenesis. Medicinal plants from Plectranthus spp. (Lamiaceae) are a well-known source of interesting abietanes, such as 7α-acetoxy-6ß-hydroxyroyleanone (Roy). This study aimed to extract and isolate Roy from P. grandidentatus Gürke, comparing two extraction methods (CO2 supercritical and ultrasound-assisted acetonic extraction), and design new royleanone derivatives for PKC modulation focusing on breast cancer therapy. The concentration of Roy in the extracts was determined by HPLC-DAD. The supercritical extraction method yielded 3.6% w/w, with the presence of 42.7 µg mg-1 of Roy (yield of 0.13%), while ultrasound-assisted acetonic extraction yielded 2.3% w/w, with the presence of 55.2 µg mg-1 of Roy (yield of 0.15%). The reactivity of Roy was investigated aiming at synthetizing new ester derivatives through standard benzoylation and esterification reactions. The benzoylated (Roy-12-Bz) and acetylated (Roy-12-Ac) derivatives in the C12 position were consistently prepared with overall good yields (33-86%). These results indicate the 12-OH position as the most reactive for esterification, affording derivatives under mild conditions. The reported di-benzoylated (RoyBz) and di-acetylated (RoyAc) derivatives were also synthesized after increasing the temperature (50 °C), reaction time, and using an excess of reagents. The cytotoxic potential of Roy and its derivatives was assessed against breast cancer cell lines, with RoyBz emerging as the most promising compound. Derivatization at position C-12 did not offer advantages over di-esterification at positions C-12 and C-6 or over the parent compound Roy and the presence of aromatic groups favored cytotoxicity. Evaluation of royleanones as PKC-α, ßI, δ, ε, and ζ activators revealed DeRoy's efficacy across all isoforms, while RoyPr showed promising activation of PKC-δ but not PKC-ζ, highlighting the influence of slight structural changes on isoform selectivity. Molecular docking analysis emphasized the importance of microenvironmental factors in isoform specificity, underscoring the complexity of PKC modulation and the need for further exploration.

A green and simple method for enrichment of major diterpenoids from the buds of Wikstroemia chamaedaphne with macroporous resins and their activation of latent human immunodeficiency virus activity.

In this study, a green and efficient enrichment method for the four majors active diterpenoid components: pimelotide C, pimelotide A, simplexin, and 6α,7α-epoxy-5ß-hydroxy-12-deoxyphorbol-13-decanoate in the buds of Wikstroemia chamaedaphne was established using macroporous resin chromatography. The adsorption and desorption rates of seven macroporous resins were compared using static tests. The D101 macroporous resin exhibited the best performance. Static and dynamic adsorption tests were performed to determine the enrichment and purification of important bioactive diterpenoids in the buds of W. chamaedaphne. Diterpenoid extracts were obtained by using D101 macroporous resin from the crude extracts of W. chamaedaphne. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis demonstrated that most of the diterpenoids were enriched in diterpenoid extracts. These results confirmed that diterpenoids in the buds of W. chamaedaphne could be enriched using macroporous resin technology, and the enriched diterpenoid extracts showed more efficient activation of the latent human immunodeficiency virus. This study provides a novel strategy for discovering efficient and low-toxicity latency-reversing agents and a potential basis for the comprehensive development and clinical application of the buds of W. chamaedaphne.

Sclareol antagonizes the sedative effect of diazepam in thiopental sodium-induced sleeping animals: In vivo and in silico studies.

BACKGROUND: Sclareol (SCL), a labdane diterpene compound found in Salvia sclarea L., exhibited therapeutic effects. This study investigated the potential interaction between SCL and diazepam (DZP) in modulating sedation in the thiopental sodium-induced sleeping animal model, supported by in-silico molecular docking analysis. METHODS: The control, sclareol (5, 10 and 20 mg/kg), and the reference drugs [diazepam: 3 mg/kg and Caffeine (CAF): 10 mg/kg] were used in male albino mice. Then, sodium thiopental (40 mg/kg, i.p.) was administrated to induce sleep. The latent period, percentage of sleep incidence and modulation of latency were measured. Further, homology modeling of human γ-aminobutyric acid (GABA) was conducted examine the binding mode of GABA interaction with SCL, DZP, and CAF compounds RESULTS: SCL (low dose) slightly increased the sleep latency, while the higher dose significantly prolonged sleep latency. DZP, a GABAA receptor agonist, exhibited strong sleep-inducing properties, reducing sleep latency, and increasing sleeping time. Caffeine (CAF) administration prolonged sleep latency and reduced sleeping time, consistent with its stimulant effects. The combination treatments involving SCL, DZP, and CAF showed mixed effects on sleep parameters. The molecular docking revealed good binding affinities of SCL, DZP, and CAF for GABAA receptor subunits A2 and A5. CONCLUSIONS: Our findings highlighted the complex interplay between SCL, DZP, and CAF in regulating sleep behaviors and provided insights into potential combination therapies for sleep disorders.

Andrographolide suppresses SARS-CoV-2 infection by downregulating ACE2 expression: A mechanistic study.

Angiotensin-converting enzyme 2 (ACE2) is the receptor that enables SARS-CoV-2 to invade host cells. Previous studies have reported that reducing ACE2 expression may have an anti-SARS-CoV-2 effect. In this study, we constructed a pGL4.10-F2-ACE2 vector with double luciferase genes (firefly and Renilla luciferase) under the control of the ACE2 promoter and used it to screen compounds from Chinese traditional medicinal herbs (CTMHs) that can inhibit ACE2 transcription in human cells. We transfected HEK293T cells with pGL4.10-F2-ACE2 and treated them with CTMH compounds and then measured fluorescence to evaluate the indirect inhibition of ACE2 transcription. Out of 37 compounds tested, andrographolide demonstrated a dose-dependent inhibition of ACE2 transcription. We further confirmed by RT-qPCR and Western blot assays that andrographolide also reduced ACE2 expression in BEAS-2B cells in a dose-dependent manner. Moreover, pseudovirus infection assays in BEAS-2B cells demonstrated that andrographolide can inhibit SARS-CoV-2 infection in a dose-dependent manner. These results suggest that andrographolide has potential anti-SARS-CoV-2 activity and could be a candidate drug for COVID-19 prevention and treatment.

Triptolide decreases podocytes permeability by regulating TET2-mediated hydroxymethylation of ZO-1.

Podocyte injury or dysfunction can lead to proteinuria and glomerulosclerosis. Zonula occludens 1 (ZO-1) is a tight junction protein which connects slit diaphragm (SD) proteins to the actin cytoskeleton. Previous studies have shown that the expression of ZO-1 is decreased in chronic kidney disease (CKD). Thus, elucidation of the regulation mechanism of ZO-1 has considerable clinical importance. Triptolide (TP) has been reported to exert a strong antiproteinuric effect by inhibiting podocyte epithelial mesenchymal transition (EMT) and inflammatory response. However, the underlying mechanisms are still unclear. We found that TP upregulates ZO-1 expression and increases the fluorescence intensity of ZO-1 in a puromycin aminonucleoside (PAN)-induced podocyte injury model. Permeablity assay showed TP decreases podocyte permeability in PAN-treated podocyte. TP also upregulates the DNA demethylase TET2. Our results showed that treatment with the DNA methyltransferase inhibitors 5-azacytidine (5-AzaC) and RG108 significantly increased ZO-1 expression in PAN-treated podocytes. Methylated DNA immunoprecipitation (MeDIP) and hydroxymethylated DNA immunoprecipitation (hMeDIP) results showed that TP regulates the methylation status of the ZO-1 promoter. Knockdown of TET2 decreased ZO-1 expression and increased methylation of its promoter, resulting in the increase of podocyte permeability. Altogether, these results indicate that TP upregulates the expression of ZO-1 and decreases podocyte permeability through TET2-mediated 5 mC demethylation. These findings suggest that TP may alleviate podocyte permeability through TET2-mediated hydroxymethylation of ZO-1.

Albiflorenes A-L, polyoxygenated cyclohex(a/e)ne diterpene esters from Kaempferia albiflora.

Twelve polyoxygenated cyclohex(a/e)ne diterpene esters, named albiflorenes A-L (1-12), were isolated from the whole plants of Kaempferia albiflora, known as "Prao Mang Mum." Their structures and relative stereochemistry were determined by extensive spectroscopic analysis. Furthermore, the comparison of experimental electronic circular dichroism (ECD) curves with the curves predicted by TDDFT was used to determine the absolute configurations. Albiflorenes contain polyoxygenated cyclohexane (or cyclohexene) derivatives, which are linked to either isopimarane or abietane diterpene acid units. The discovery marks the first occurrence of a conjugate between polyoxygenated cyclohexane (or cyclohexene) rings and diterpenoids. Among the isolates, albiflorene C specifically exhibited antibacterial activity against Bacillus cereus with MIC and MBC values of 3.13 and 6.25 µg/mL, respectively.

Kallopterolides A-I, a New Subclass of seco-Diterpenes Isolated from the Southwestern Caribbean Sea Plume Antillogorgia kallos.

Kallopterolides A-I (1-9), a family of nine diterpenoids possessing either a cleaved pseudopterane or a severed cembrane skeleton, along with several known compounds were isolated from the Caribbean Sea plume Antillogorgia kallos. The structures and relative configurations of 1-9 were characterized by analysis of HR-MS, IR, UV, and NMR spectroscopic data in addition to computational methods and side-by-side comparisons with published NMR data of related congeners. An investigation was conducted as to the potential of the kallopterolides as plausible in vitro anti-inflammatory, antiprotozoal, and antituberculosis agents.

Combining the Elicitor Up-Regulated Production of Unusual Linear Diterpene-Derived Variants for an In-Depth Assessment of the Application Value and Risk of the Medicinal and Edible Basidiomycete Schizophyllum commune.

To better assess the practical value and avoid potential risks of the traditionally medicinal and edible basidiomycete Schizophyllum commune, which may arise from undescribed metabolites, a combination of elicitors was introduced for the first time to discover products from cryptic and low-expressed gene clusters under laboratory cultivation. Treating S. commune NJFU21 with the combination of five elicitors led to the upregulated production of a class of unusual linear diterpene-derived variants, including eleven new ones (1-11), along with three known ones (12-14). The structures and stereochemistry were determined by 1D and 2D NMR, HRESIMS, ECD, OR and VCD calculations. Notably, the elongation terminus of all the diterpenes was decorated by an unusual butenedioic acid moiety. Compound 1 was a rare monocyclic diterpene, while 2-6 possessed a tetrahydrofuran moiety. The truncated metabolites 4, 5 and 13 belong to the trinorditerpenes. All the diterpenes displayed approximately 70% scavenging of hydroxyl radicals at 50 µM and null cytotoxic activity at 10 µM. In addition, compound 1 exhibited potent antifungal activity against the plant pathogenic fungi Colletotrichum camelliae, with MIC values of 8 µg/mL. Our findings indicated that this class of diterpenes could provide valuable protectants for cosmetic ingredients and the lead compounds for agricultural fungicide development.

Tigilanol Tiglate-Induced Changes in Secretome Profiles Alter C-Met Phosphorylation and Cell Surface Protein Expression in H357 Head and Neck Cancer Cells.

Tigilanol tiglate (TT, also known as EBC-46) is a novel, plant-derived diterpene ester possessing anticancer and wound-healing properties. Here, we show that TT-evoked PKC-dependent S985 phosphorylation of the tyrosine kinase MET leads to subsequent degradation of tyrosine phosphorylated p-Y1003 and p-Y1234/5 MET species. PKC inhibition with BIM-1 blocked S985 phosphorylation of MET and led to MET cell surface accumulation. Treatment with metalloproteinase inhibitors prevented MET-ECD release into cell culture media, which was also blocked by PKC inhibitors. Furthermore, unbiased secretome analysis, performed using TMT-technology, identified additional targets of TT-dependent release of cell surface proteins from H357 head and neck cancer cells. We confirm that the MET co-signalling receptor syndecan-1 was cleaved from the cell surface in response to TT treatment. This was accompanied by rapid cleavage of the cellular junction adhesion protein Nectin-1 and the nerve growth factor receptor NGFRp75/TNFR16. These findings, that TT is a novel negative regulator of protumorigenic c-MET and NGFRp75/TNFR16 signalling, as well as regulating Nectin-1-mediated cell adhesion, further contribute to our understanding of the mode of action and efficacy of TT in the treatment of solid tumours.

Methods for the preparation and analysis of a bifunctional class II diterpene synthase, copalyl diphosphate synthase from Penicillium fellutanum.

Terpenes comprise the largest class of natural products and are used in applications spanning the areas of medicine, cosmetics, fuels, flavorings, and more. Copalyl diphosphate synthase from the Penicillium genus is the first bifunctional terpene synthase identified to have both prenyltransferase and class II cyclase activities within the same polypeptide chain. Prior studies of bifunctional terpene synthases reveal that these systems achieve greater catalytic efficiency by channeling geranylgeranyl diphosphate between the prenyltransferase and cyclase domains. A molecular-level understanding of substrate transit phenomena in these systems is highly desirable, but a long disordered polypeptide segment connecting the prenyltranferase and cyclase domains thwarts the crystallization of full-length enzymes. Accordingly, these systems are excellent candidates for structural analysis using cryo-electron microscopy (cryo-EM). Notably, these systems form hexameric or octameric oligomers, so the quaternary structure of the full-length enzyme may influence substrate transit between catalytic domains. Here, we describe methods for the preparation of bifunctional hexameric copalyl diphosphate synthase from Penicillium fellutanum (PfCPS). We also outline approaches for the preparation of cryo-EM grids, data collection, and data processing to yield two-dimensional and three-dimensional reconstructions.

Methods for the preparation and analysis of the diterpene cyclase fusicoccadiene synthase.

Prenyltransferases are terpene synthases that combine 5-carbon precursor molecules into linear isoprenoids of varying length that serve as substrates for terpene cyclases, enzymes that catalyze fascinating cyclization reactions to form diverse terpene natural products. Terpenes and their derivatives comprise the largest class of natural products and have myriad functions in nature and diverse commercial uses. An emerging class of bifunctional terpene synthases contains both prenyltransferase and cyclase domains connected by a disordered linker in a single polypeptide chain. Fusicoccadiene synthase from Phomopsis amygdali (PaFS) is one of the most well-characterized members of this subclass and serves as a model system for the exploration of structure-function relationships. PaFS has been structurally characterized using a variety of biophysical techniques. The enzyme oligomerizes to form a stable core of six or eight prenyltransferase domains that produce a 20-carbon linear isoprenoid, geranylgeranyl diphosphate (GGPP), which then transits to the cyclase domains for the generation of fusicoccadiene. Cyclase domains are in dynamic equilibrium between randomly splayed-out and prenyltransferase-associated positions; cluster channeling is implicated for GGPP transit from the prenyltransferase core to the cyclase domains. In this chapter, we outline the methods we are developing to interrogate the nature of cluster channeling in PaFS, including enzyme activity and product analysis assays, approaches for engineering the linker segment connecting the prenyltransferase and cyclase domains, and structural analysis by cryo-EM.

Mechanistic characterisation of the diterpene synthase for clitopilene and identification of isopentalenene synthase from the fungus Clitopilus passeckerianus.

Two terpene synthases from the pleuromutilin producing fungus Clitopilus passeckerianus were functionally characterised. The first enzyme CpTS1 produces the new diterpene clitopilene with a novel 6-6-5-5 tetracyclic skeleton, while the second enzyme CpTS2 makes the new sesquiterpene isopentalenene. The CpTS1 reaction mechanism was studied in depth using experimental and theoretical approaches.